The Piperno eutaxitic tuff, 20 m thick, interfingered with loose lithic-rich breccia, that outcrops at the base of Camaldoli hill (Campi Flegrei) (De Lorenzo, 1904) was interpreted by Rittmann (1950) to be a local air fall tuff. This welded tuff was reinterpreted by Rosi et al. (1996) as a pyroclastic flow and was considered as the proximal facies of the 39 ka Campanian Ignimbrite (CI), the largest explosive eruption of the past 200 ka in Europe. According to Rolandi (1988) and Rolandi et al. (2003), the products of this eruption gave rise to a complex formation, subdivided into two units. CI unit-1, present at the base, is the main deposit of the eruption, widely dispersed regionally as a low-aspect-ratio ignimbrite (Walker, 1983) and identified also in the field as Campanian Gray Tuff (CGT) (Di Girolamo, 1968a; 1970; Rolandi et al., 2003). CI unit-2, which overlies the first one, is identified in the field as the well-known PipernoeMuseumBreccia sequence. CI unit-2 is originated from discrete source areas and is distributed over limited distances in the Campanian Plain. In contrast to CI unit-1, CI unit-2 has the characteristics of a high aspect ratio ignimbrite (Rolandi et al., 2003) . On the basis of the field distribution, the Piperno layers cannot be considered as the proximal facies of CGT. The fact that the Piperno has a thickness of just 20 m at the base of the Camaldoli Hill is not compatible for a proximal facies for an eruption of 250e300 km3. Furthermore, it neither occupies with continuity the edge of a hypothetical 39 ka caldera nor it is present as a caldera filling welded tuff and lava-like ignimbrites. This last important aspect emerges from chronostratigraphy reconstructed by deep drill holes (500 m) performed in the Campi Flegrei (De Natale et al., 2017), whose stratigraphic column does not show the presence of such a deposit, underlying the nearby Posillipo Hill, in the same way as it is present at the base of Camaldoli Hill. Based on this evidence, we can conclude that CI unit-1 (CGT) was not formed 39 ka ago from caldera activity; the only currently apparent caldera is that of the 15 ka Neapolitan Yellow Tuff (NYT) eruption (Di Girolamo et al., 1984; Rolandi et al., 2019, this volume). The source area of the main 39 ka CI eruption must be located outside of the Campi Flegrei caldera. We emphasize here the important role of extensional faults located in the Campanian Plain in localizing the CI magmatic activity (Rolandi et al., 2003; Bellucci et al., 2006; Milia and Torrente, 2011). Our goal was to reconstruct the distribution of CI unit-1 in the northern Campanian Plain. As this unit is completely buried and thickest beneath the plain, several drillings have been carried out, which sampled its products to the base. From this drill hole data, we have identified a new facies of highly welded CGT in the Giugliano area, which could suggest that it is the source area. Moreover, this study is focused on lateral and vertical variations of welding degree and the distribution of CI unit-1, also analyzing its ability to surmount Apennine chain barriers.
The 39 ka campanian ignimbrite eruption: New data on source area in the campanian plain
Somma Renato;
2019
Abstract
The Piperno eutaxitic tuff, 20 m thick, interfingered with loose lithic-rich breccia, that outcrops at the base of Camaldoli hill (Campi Flegrei) (De Lorenzo, 1904) was interpreted by Rittmann (1950) to be a local air fall tuff. This welded tuff was reinterpreted by Rosi et al. (1996) as a pyroclastic flow and was considered as the proximal facies of the 39 ka Campanian Ignimbrite (CI), the largest explosive eruption of the past 200 ka in Europe. According to Rolandi (1988) and Rolandi et al. (2003), the products of this eruption gave rise to a complex formation, subdivided into two units. CI unit-1, present at the base, is the main deposit of the eruption, widely dispersed regionally as a low-aspect-ratio ignimbrite (Walker, 1983) and identified also in the field as Campanian Gray Tuff (CGT) (Di Girolamo, 1968a; 1970; Rolandi et al., 2003). CI unit-2, which overlies the first one, is identified in the field as the well-known PipernoeMuseumBreccia sequence. CI unit-2 is originated from discrete source areas and is distributed over limited distances in the Campanian Plain. In contrast to CI unit-1, CI unit-2 has the characteristics of a high aspect ratio ignimbrite (Rolandi et al., 2003) . On the basis of the field distribution, the Piperno layers cannot be considered as the proximal facies of CGT. The fact that the Piperno has a thickness of just 20 m at the base of the Camaldoli Hill is not compatible for a proximal facies for an eruption of 250e300 km3. Furthermore, it neither occupies with continuity the edge of a hypothetical 39 ka caldera nor it is present as a caldera filling welded tuff and lava-like ignimbrites. This last important aspect emerges from chronostratigraphy reconstructed by deep drill holes (500 m) performed in the Campi Flegrei (De Natale et al., 2017), whose stratigraphic column does not show the presence of such a deposit, underlying the nearby Posillipo Hill, in the same way as it is present at the base of Camaldoli Hill. Based on this evidence, we can conclude that CI unit-1 (CGT) was not formed 39 ka ago from caldera activity; the only currently apparent caldera is that of the 15 ka Neapolitan Yellow Tuff (NYT) eruption (Di Girolamo et al., 1984; Rolandi et al., 2019, this volume). The source area of the main 39 ka CI eruption must be located outside of the Campi Flegrei caldera. We emphasize here the important role of extensional faults located in the Campanian Plain in localizing the CI magmatic activity (Rolandi et al., 2003; Bellucci et al., 2006; Milia and Torrente, 2011). Our goal was to reconstruct the distribution of CI unit-1 in the northern Campanian Plain. As this unit is completely buried and thickest beneath the plain, several drillings have been carried out, which sampled its products to the base. From this drill hole data, we have identified a new facies of highly welded CGT in the Giugliano area, which could suggest that it is the source area. Moreover, this study is focused on lateral and vertical variations of welding degree and the distribution of CI unit-1, also analyzing its ability to surmount Apennine chain barriers.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
